Indirectly heated hot-cathodes with pink ruby insulator

ABSTRACT

An indirectly heated hot-cathode has a metallic cathode sleeve having inner walls defining a cavity. An electric heating element is arranged in the cavity defined by the cathode sleeve. The necessary electrical insulation between the heating element and the cathode sleeve is maintained by an insulating member shaped to conform to and arranged to at least partially cover the inner walls of the cathode sleeve, and constructed of a material selected from the group consisting of ruby, quartz and sapphire.

United States Patent Held [4 Mar. 28, 1972 s41 INDIRECTLY HEATED HOT- 1,878,089 9/1932 Albersheim ..313/340 x CATHODES WITH PINK RUBY 3,160,780 12/1964 Coppola... ....313/340 X 2,227,017 12/1940 Schlesinger... ....313/340 X INSULATOR 2,817,784 l2/1957 Katz ..313/340 [72] Inventor: Walter Held, Gunzburg, Germany FOREIGN PATENTS OR APPLICATIONS [73] Ass1gnee: Licentia Patent-Verwaltungs G.m.b.H.,

Frankfurt Germany 1,090,774 10/1960 Germany ..313/340 Filed! June 1970 Primary Examiner-David Schonberg Assistant Examiner-Toby I-i. Kusmer [21] Appl' SL298 Attorney- -Spencer& Kaye [30] Foreign Application Priority Data [57] ABSTRACT July 1, 1969 Germany ..P 19 33 309.6 An indirectly heated ath d as a m talli cath e sleeve having inner walls defining a cavity. An electric heating 521 U.S. c1 ..313/340- element arranged in the cavity defined by the cathode 5 .101 1245011- 19/18 sleeve. The necessary electrical insulation between the heat- [58] Field f s 313/337, 340 ing element and the cathode sleeve is maintained by an insulating member shaped to conform to and arranged to at least 56] References Cited partially cover the inner walls of the cathode sleeve, and constructed of a material selected from the group consisting of UNITED STATES PATENTS y, quartz and s pphire- 2,870,366 1/1959 Van To] ..313/340 X 3 Claims, 8 Drawing Figures Inventor. Walter Held z monnsvs.

P'ATENTEDMAR28 I972 BY/J i Fig. 5 /5 d Q I s l i INDIRECTLY HEATED I'IOT-CATI-IODES WITH PINK RUBY IN SULATOR BACKGROUND OF THE INVENTION The present invention relates to an indirectly heated hotcathode for an electric discharge device such as a cathode-ray tube. The cathode has an electric heating element arranged in a cavity of a metallic cathode sleeve in an electrically insulated manner with respect to the cathode sleeve. The inner walls of the cavity are at least partially covered with a prefabricated insulating part, generally shaped as a cylinder.

Normally, hot-cathodes are constructed of a so-called cathode sleeve of metal and bearing a suitable emission material. The cathode sleeve is provided with a cavity in which an electrically heatable element is disposed. A very good electrical insulation must exist between the electric heating element and the metallic cathode sleeve. This electric insulation must meet high standards due to the high temperatures encountered during operation of the cathode. For dispenser cathodes in particular, it is desired to obtain very high operating temperatures, for example, between 900 and l,200 C. The electrical insulation values previously realized were often not sufficient.

In addition to the usual insulation of the heating element itself, which is generally accomplished by the direct coating of the heating wire with a ceramic material, it has been proposed to provide the inner walls of the cavity of the cathode sleeve with an electrically insulating coating. However, it has been found that in such arrangements the heat transfer from the heating element to the cathode sleeve is not always satisfacto- SUMMARY OF THE INVENTION It is an object of the present invention to provide a novel hot-cathode which is particularly improved with respect to the abovementioned disadvantages.

The present invention provides that the insulating coating be in the form of a prefabricated cylindrical insert which may be at least partially closed at one end, constructed of ruby, sapphire or quartz.

With the use of a prefabricated insulating cylinder made of ruby, sapphire, or quartz, it is possible to achieve outstanding electrical insulating properties. Even when very high temperatures are used, the insulating properties of such insulating inserts are not significantly impaired. A further advantage is achieved in that, due to the inherent characteristics of these materials, a relatively good heat transfer between the cathode sleeve and the heating element is assured. In addition, the manufacture of a hot-cathode according to the present invention is also relatively simple and inexpensive.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional elevational view of a hot-cathode according to the present invention.

FIGS. 2-8 are cross-sectional, elevation views showing various embodiments of a prefabricated cylindrical insert having good electrical insulating properties according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The cathode sleeve of the hot-cathode shown in FIG. 1 of the drawings has a pressed metal cathode sleeve 1 having inner walls 2 defining a cavity 3. One end of cathode sleeve 1 is closed and folded in such a manner that a cathode cup 4 is formed, into which suitable known emission material 5 is pressed. Cathode sleeve 1 may be of any suitable known metal such as nickel or molybdenum. Material 5 may be, for example, powdered tungsten, molybdenum, nickel, tantalum, iridium or rhodium, or mixtures thereof, mixed with an emitting material in a known matter. This particular cathode is a socalled reservoir cathode. It is understood, of course, that any suitable, well-known type of indirectly heated, hot-cathode r ma employ the present invention.

0 are covered at least in part, according to the present invention, with a cylindrical insulating member 7, which is constructed of a material such as ruby, sapphire or quartz. Member 7 is prefabricated in a known manner by an appropriate squeezing operation as a separate member and is then inserted into the cavity 3 of cathode sleeve 1. The member 7 of FIG. 1 is shown separately in cross section in FIG. 2 and is in the form of a cylinder enclosed at one end by a flat portion 7.

FIGS. 3-8 show additional preferred embodiments of electrical insulating members which may be inserted into an appropriate cathode sleeve.

The embodiments shown in FIGS. 3 and 4 have cylindrical bodies 8 enclosed at one end, but, in contradistinction to the embodiment of FIG. 2, the enclosed end is rounded at 9. In addition, the embodiment of FIG. 4 defines an opening 10 in the enclosed end.

The embodiment shown in FIG. 5 has a cylindrical body 11 having a groove 12 defined near one end thereof. This groove 12 serves to provide an anchorage between the respective cathode sleeve (not shown) and the insulating member 11. That is, the cathode sleeve has a mating groove which engages groove 12.

In the embodiment shown in FIGS. 6 and 7, the cylindrical members 13 and 14 are provided with respective cover members l5 and 16. These cover members 15 and 16 are also preferably constructed of sapphire, ruby or quartz, but can also be made of any other suitable known material. The two part construction of the embodiments shown in FIGS. 6 and 7 is advantageous because they may be easier and less expensive to fabricate than the embodiments of FIGS. 2-5.

FIG. 8 shows another embodiment which is easy to fabricate in that it is simply a cylinder 17 having both ends open.

Although ruby, sapphire, or quartz may be used to constructed the insertable electrically insulating members such as 7 of FIG. 1, pink ruby has proven to be particular by preferable. This is because pink ruby exhibits particularly favorable heat transfer properties. The use of pink ruby to construct the insertable electrical insulating member, therefore, represents a particularly preferred embodiment of the present invention.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

I claim:

1. An indirectly heated hot-cathode, comprising, in combination: I

a. a metallic cathode sleeve having inner walls defining a cavity;

b. an electric heating element arranged in the cavity defined by said cathode sleeve; and

c. an insulating member for electrically insulating said heating element from said cathode sleeve shaped to conform to and arranged in said cavity to at least partially cover said inner walls of said cathode sleeve, and constructed of a pink ruby material.

2. A hot-cathode as defined in claim 1, wherein said insulating member has two ends and is at least partially enclosed at one end.

3. A hot-cathode as defined in claim 2, wherein said cathode sleeve is a reservoir cathode defining a cathode cup. 

1. An indirectly heated hot-cathode, comprising, in combination: a. a metallic cathode sleeve having inner walls defining a cavity; b. an electric heating elemenT arranged in the cavity defined by said cathode sleeve; and c. an insulating member for electrically insulating said heating element from said cathode sleeve shaped to conform to and arranged in said cavity to at least partially cover said inner walls of said cathode sleeve, and constructed of a pink ruby material.
 2. A hot-cathode as defined in claim 1, wherein said insulating member has two ends and is at least partially enclosed at one end.
 3. A hot-cathode as defined in claim 2, wherein said cathode sleeve is a reservoir cathode defining a cathode cup. 